2.) Extell Development closed on its acquisition of a four-story mixed-use building on the Upper East Side from Seligman Roseberg’s Montrose Associates for $16.2 million. The property, at 1514 First Avenue, contains seven apartments and two commercial units. The parcel is the corner property in an assemblage that Extell has been accumulating over the past decade . The developer is gathering an assemblage spanning more than 250,000 buildable square feet.